This invention relates to tunable, radio frequency, waveguide devices for use in broadband wireless, and other telecommunications applications.
The use of broadband wireless communication systems has increased in the last decade, crowding the available radio frequency spectrum and creating a need for higher to rejection between adjacent channels. Higher rejection requires either more complex filters with higher loss and higher cost, or narrower bandwidth filters resulting in the need for more discreet filter designs to accommodate the full radio spectrum.
Radio manufacturers are forced to make trade-offs between performance requiring more complex designs or more inventory and lower cost requiring broader bandwidths and lower signal-to-noise ratios.
Electronically tunable filter designs are now possible through the advent tunable dielectric materials. These materials, that change dielectric properties through the application of a DC bias voltage, can be used in the resonator of a filter structure allowing the filter to be electronically tuned across broad frequency bands. This opens the possibility of replacing many narrow band, fixed frequency designs with a single tunable design, thereby reducing inventory and associated costs without sacrificing performance or increasing unit cost. Examples of filters including tunable dielectric materials are shown in U.S. patent application Ser. No. 09/734,969 (International Publication No. WO 00/35042 A1), the disclosure of which is hereby incorporated by reference.
Tunable dielectric materials are materials whose permittivity (more commonly called dielectric constant) can be varied by varying the strength of an electric field to which the materials are subjected. Even though these materials work in their paraelectric phase above the Curie temperature, they are conveniently called xe2x80x9cferroelectricxe2x80x9d because they exhibit spontaneous polarization at temperatures below the Curie temperature. Tunable ferroelectric materials including barium-strontium titanate (BSTO) or BSTO composites have been the subject of several patents.
Dielectric materials including barium strontium titanate are disclosed in U.S. Pat. No. 5,312,790 to Sengupta, et al. entitled xe2x80x9cCeramic Ferroelectric Materialxe2x80x9d; U.S. Pat. No. 5,427,988 to Sengupta, et al. entitled xe2x80x9cCeramic Ferroelectric Composite Material-BSTO-MgOxe2x80x9d; U.S. Pat. No. 5,486,491 to Sengupta, et al. entitled xe2x80x9cCeramic Ferroelectric Composite Material-BSTO-ZrO2xe2x80x9d; U.S. Pat. No. 5,635,434 to Sengupta, et al. entitled xe2x80x9cCeramic Ferroelectric Composite Material-BSTO-Magnesium Based Compoundxe2x80x9d; U.S. Pat. No. 5,830,591 to Sengupta, et al. entitled xe2x80x9cMultilayered Ferroelectric Composite Waveguidesxe2x80x9d; U.S. Pat. No. 5,846,893 to Sengupta, et al. entitled xe2x80x9cThin Film Ferroelectric Composites and Method of Makingxe2x80x9d; U.S. Pat. No. 5,766,697 to Sengupta, et al. entitled xe2x80x9cMethod of Making Thin Film Compositesxe2x80x9d; U.S. Pat. No. 5,693,429 to Sengupta, et al. entitled xe2x80x9cElectronically Graded Multilayer Ferroelectric Compositesxe2x80x9d; U.S. Pat. No. 5,635,433 to Sengupta, entitled xe2x80x9cCeramic Ferroelectric Composite Material-BSTO-ZnOxe2x80x9d; and U.S. Pat. No. 6,074,971 by Chiu et al. entitled xe2x80x9cCeramic Ferroelectric Composite Materials with Enhanced Electronic Properties BSTO-Mg Based Compound-Rare Earth Oxidexe2x80x9d. These patents are hereby incorporated by reference. The materials shown in these patents, especially BSTO-MgO composites, show low dielectric loss and high tunability. Tunability is defined as the fractional change in the dielectric constant with applied voltage.
In addition, the following U.S. Patent Applications, assigned to the assignee of this application, disclose additional examples of tunable dielectric materials: U.S. application Ser. No. 09/594,837 filed Jun. 15, 2000, entitled xe2x80x9cElectronically Tunable Ceramic Materials Including Tunable Dielectric and Metal Silicate Phasesxe2x80x9d (International Publication No. WO 01/96258 A1); U.S. application Ser. No. 09/768,690 filed Jan. 24, 2001, entitled xe2x80x9cElectronically Tunable, Low-Loss Ceramic Materials Including a Tunable Dielectric Phase and Multiple Metal Oxide Phasesxe2x80x9d; U.S. application Ser. No. 09/882,605 filed Jun. 15, 2001, entitled xe2x80x9cElectronically Tunable Dielectric Composite Thick Films And Methods Of Making Samexe2x80x9d (International Publication No. WO 01/99224 A1); U.S. application Ser. No. 09/834,327 filed Apr. 13, 2001, entitled xe2x80x9cStrain-Relieved Tunable Dielectric Thin Filmsxe2x80x9d; and U.S. Provisional Application Serial No. 60/295,046 filed Jun. 1, 2001 entitled xe2x80x9cTunable Dielectric Compositions Including Low Loss Glass Fritsxe2x80x9d. These patent applications are incorporated herein by reference.
U.S. patent application Ser. No. 09/838,483 (International Publication No. WO 01/82404 A1) discloses a waveguide-finline tunable phase shifter and is hereby incorporated by reference.
For maximum performance over broad operating temperature ranges the temperature of a radio frequency component using electronically tuned material must be controlled by passive temperature compensation and/or active thermal control. Active thermal control requires either injection or extraction of heat, which may be highly inefficient unless proper precautions are taken to isolate the filter from the thermal environment.
There is a need for tunable electronic devices that can operate in a variable temperature environment, while maintaining satisfactory electronic operation.
Electronic devices constructed in accordance with this invention include a non-metallic waveguide, a tunable component mounted within the waveguide, and a conductive layer on a surface of the waveguide. The tunable component can comprise a tunable filter. The non-metallic waveguide can comprise a plastic material. Connections for applying a tuning voltage to the tunable component can be provided. The conductive layer can comprise a metal. A temperature sensor can be connected to the waveguide to provide a signal representative of the temperature of the device. That signal can be used to control an associated temperature control unit.